1. Technical Field
This application relates to computer storage devices, and more particularly to communication between storage devices.
2. Description of Related Art
Host processor systems may store and retrieve data using a storage device containing a plurality of host interface units (host adapters), disk drives, and disk interface units (disk adapters). Such storage devices are provided, for example, by EMC Corporation of Hopkinton, Mass. and disclosed in U.S. Pat. No. 5,206,939 to Yanai et al., U.S. Pat. No. 5,778,394 to Galtzuret al., U.S. Pat. No. 5,845,147 to Vishlitzky et al., and U.S. Pat. No. 5,857,208 to Ofek. The host systems access the storage device through a plurality of channels provided therewith. Host systems provide data and access control information through the channels to the storage device and the storage device provides data to the host systems also through the channels. The host systems do not address the disk drives of the storage device directly, but rather, access what appears to the host systems as a plurality of logical disk units. The logical disk units may or may not correspond to the actual disk drives. Allowing multiple host systems to access the single storage device unit allows the host systems to share data stored therein.
In some instances, it may be desirable to copy data from one storage device to another. For example, if a host writes data to a first storage device, it may be desirable to copy that data to a second storage device provided in a different location so that if a disaster occurs that renders the first storage device inoperable, the host (or another host) may resume operation using the data of the second storage device. Such a capability is provided, for example, by the Remote Data Facility (RDF) product provided by EMC Corporation of Hopkinton, Mass. With RDF, a user may denote a first storage device as a master storage device and a second storage device as a slave storage device. Other incarnations of RDF may provide a peer to peer relationship between the local and remote storage devices. The host interacts directly with the local storage device, but any data changes made to the local storage device are automatically provided to a remote storage device using RDF. The local and remote storage devices may be connected by a data link, such as an ESCON link or a Fiber Channel link. The RDF functionality may be facilitated with an RDF adapter (RA) provided at each of the storage devices.
In some instances, it may be desirable to modify the RDF configuration system. However, in many cases, such modifications require skilled technicians using special software and non-standard connections to the local storage devices. It is desirable to automate the RDF configuration modification process to allow a host to modify the RDF configuration. In addition, it is desirable that allowing dynamic modifications to RDF configuration will not effect operation of the storage device when individual devices therein need to access the dynamic configuration information.
According to the present invention, determining device characteristics includes obtaining a first globally accessible value, if the first globally accessible value corresponds to a stored first value, obtaining device characteristics data from a relatively fast memory, if the first globally accessible value does not correspond to the stored first value, obtaining a second globally accessible value, if the second globally accessible value corresponds to a stored second value, obtaining device characteristics data from a relatively fast memory, if the second globally accessible value does not correspond to the stored second value, obtaining device characteristics data from a relatively slow memory and updating the relatively fast memory, the stored first value, and the stored second value. The globally accessible first value may include device I/O information. The globally accessible values may be stored in global memory that is accessible to a plurality of processors. The relatively slow memory may be global memory that is accessible to a plurality of processors. The relatively fast memory may be local to a processor that accesses the first and second stored values. The second stored value may indicate whether a device is a source or a destination for data in a remote data communication link.
According further to the present invention, accessing a device includes obtaining status information that indicates how to access the device, examining at least a portion of the status information to determine if configuration of the device has changed, if the configuration of the device has not changed, accessing stored configuration data from relatively fast memory, and if the configuration of the device has changed, accessing new configuration information from relatively slow memory and updating the stored configuration data with the new configuration information. The relatively slow memory may be global memory that is accessible to a plurality of processors. The relatively fast memory may be local to a processor that accesses the fast memory. The stored configuration data may indicate whether a device is a source or a destination for data in a remote data communication link. Examining at least a portion of the status information may include determining whether the portion of the status information is equal to a first stored value. Accessing a device may also include, if the portion of the status information is not equal to the first stored value, obtaining additional status information and determining if a portion of the additional status information is equal to a second stored value. Accessing a device may also include following updating the stored configuration data, updating the first and second stored values.
According further to the present invention, a computer program product that determines device characteristics, includes executable code that obtains a first globally accessible value, executable code that obtains device characteristics data from a relatively fast memory if the first globally accessible value corresponds to a stored first value, executable code that obtains a second globally accessible value if the first globally accessible value does not correspond to the stored first value, executable code that obtains device characteristics data from a relatively fast memory if the second globally accessible value corresponds to a stored second value, and executable code that obtains device characteristics data from a relatively slow memory and updates the relatively fast memory, the stored first value, and the stored second value if the second globally accessible value does not correspond to the stored second value. The globally accessible first value may include device I/O information. The second stored value may indicate whether a device is a source or a destination for data in a remote data communication link.
According further to the present invention, a computer program product that accesses a device includes executable code that obtains status information that indicates how to access the device, executable code that examines at least a portion of the status information to determine if configuration of the device has changed, executable code that accesses stored configuration data from relatively fast memory if the configuration of the device has not changed, and executable code that accesses new configuration information from relatively slow memory and updates the stored configuration data with the new configuration information if the configuration of the device has changed. The stored configuration data may indicate whether a device is a source or a destination for data in a remote data communication link. Executable code that examines at least a portion of the status information may include executable code that determines whether the portion of the status information is equal to a first stored value. A computer program product that accesses a device may also include executable code that obtains additional status information and determines if a portion of the additional status information is equal to a second stored value if the portion of the status information is not equal to the first stored value. A computer program product that accesses a device may also include executable code that updates the first and second stored values following updating the stored configuration data.
According further to the present invention, an apparatus that determines device characteristics includes means for obtaining a first globally accessible value, means for obtaining device characteristics data from a relatively fast memory if the first globally accessible value corresponds to a stored first value, means for obtaining a second globally accessible value if the first globally accessible value does not correspond to the stored first value, means for obtaining device characteristics data from a relatively fast memory if the second globally accessible value corresponds to a stored second value, means for obtaining device characteristics data from a relatively slow memory and updating the relatively fast memory, the stored first value, and the stored second value if the second globally accessible value does not correspond to the stored second value. The globally accessible first value may include device I/O information. The globally accessible values may be stored in global memory that is accessible to a plurality of processors. The relatively slow memory may be global memory that is accessible to a plurality of processors. The relatively fast memory may be local to a processor that accesses the first and second stored values. The second stored value may indicate whether a device is a source or a destination for data in a remote data communication link.
According further to the present invention an apparatus that accesses a device, includes means for obtaining status information that indicates how to access the device, means for examining at least a portion of the status information to determine if configuration of the device has changed, means for accessing stored configuration data from relatively fast memory if the configuration of the device has not changed, and means for accessing new configuration information from relatively slow memory and updating the stored configuration data with the new configuration information if the configuration of the device has changed. The relatively slow memory may be global memory that is accessible to a plurality of processors. The relatively fast memory may be local to a processor that accesses the fast memory. The stored configuration data may indicate whether a device is a source or a destination for data in a remote data communication link. Means for examining at least a portion of the status information may include means for determining whether the portion of the status information is equal to a first stored value. The apparatus may further include means for obtaining additional status information and determining if a portion of the additional status information is equal to a second stored value if the portion of the status information is not equal to the first stored value. The apparatus may further include means for updating the first and second stored values following updating the stored configuration data.